1. Field of the Invention
The present invention relates to a method for making an amorphous soft magnetic core using Fe-based amorphous metal powders, and more particularly, to a method for making amorphous metal powder by crushing amorphous ribbons produced using a rapid solidification process (RSP), which possesses an excellent direct-current overlapping characteristic at a flow of large current and an excellent core loss, and a method for making an amorphous soft magnetic core by using the amorphous metal powders.
2. Description of the Related Art
In general, a Fe-based amorphous soft magnetic body which is used as a conventional high-frequency soft magnetic body has a high saturation magnetic flux density (Bs), but has a low magnetic permeability, a large magnetic deformation, and an inferior high-frequency characteristic. A Co-based amorphous soft magnetic body has a low saturation magnetic flux density and a drawback of an expensive raw material. In case of an amorphous soft magnetic alloy, it is difficult to shape it in the form of a strip, and is limited to form a product of a toroidal shape. Since a ferrite soft magnetic body has a low high-frequency loss and a small saturation magnetic flux density, it is difficult to accomplish a compact product. Both of the amorphous and ferrite soft magnetic body has bad reliability in thermal stability due to a low crystallization temperature.
An amorphous ribbon fabricated by a rapid solidification process (RSP) is wound to then be used as a soft magnetic core. In this case, the soft magnetic core has a remarkably low direct-current overlapping characteristic and a remarkably low high-frequency characteristic, as well as an inferior core loss. This is because a powder core product has an effect of uniformly distributing an air gap by forming an insulating layer between powder particles, but has no air gaps in the case of an amorphous ribbon wound core. Thus, a core which is formed by using an amorphous ribbon in order to improve a direct-current overlapping characteristic, has a thin gap. In this case, an efficiency is lowered and an electromagnetic wave can be influenced to other electronic products and the human body, due to a leakage flux produced from the gap.
Soft magnetic cores which are used in choke coils for suppressing or smoothing electronic noise are manufactured in a manner that ceramic insulation materials are coated on magnetic metal powder such as pure iron, Fe—Si—Al alloy (referred to as “Sendust” hereinbelow), Ni—Fe—Mo Permally (referred to as “MPP (Moly Permally Powder)” hereinbelow), and Ni—Fe Permally (referred to as “High Flux” hereinbelow), and then forming lubricants are added on the coated metal powder, to then be formed by pressure and thermally treated.
In the conventional art, an insulation layer is formed between powder particles during making a soft magnetic core, to thereby uniformly distribute an air gap. Accordingly, an Eddy current loss sharply increasing at high-frequency is minimized, and the air gap is maintained in whole, to thereby accomplish an excellent direct-current overlapping characteristic at large current.
For example, a pure iron powder core is used for a choke coil in a switching mode power supply (SMPS) having a switching frequency of 50 kHz or lower, in order to suppress electronic noise generated by overlapping high-frequency current. A “Sendust” core is used as a core for a secondary smoothing choke coil or noise suppression in a SMPS having a switching frequency of a range from 100 kHz to 1 MHz.
MPP and “High Flux” cores are used at a frequency range equal to that of the “Sendust” core, and have a more excellent direct-current overlapping characteristic and a lower core loss characteristic than those of the “Sendust” core, but have a drawback that the cores are expensive.
Recently, the soft magnetic core requires more complicated characteristics according to compactness, integration, and high reliability of a switching mode power supply (SMPS).
The characteristics required for a smoothing choke coil in a SMPS are proper inductance L, a low core loss and an excellent direct-current overlapping characteristic.
Here, a direct-current overlapping characteristic is a magnetic core characteristic with respect to a waveform formed by feeble alternating-current, generated during converting an alternating-current input of a power supply into a direct-current, on which direct-current is overlapped. In the case that direct-current is overlapped over alternating-current, a core magnetic permeability is lowered in proportion with the direct-current. Here, the direct-current overlapping characteristic is estimated in a ratio (% μ-percent permeability) represented as a direct-current overlapping permeability with respect to a permeability at the state where direct-current is not overlapped,
Thus, a variety of metal powder is employed in making a smoothing choke core in a SMPS (Switching Mode Power Supply) in various forms for each use, considering a price, a core loss, a direct-current overlapping characteristic, and a core size.